Annular spaces downhole are typically sealed with packers. Packers can be used in cased or open hole. One type of packer involves an element mounted to a mandrel, where the element is made of an elastomer. The packer is placed downhole and can be set by mechanical compression of the element. The longitudinal mechanical compression increases the diameter. Another technique has been to simply expand the mandrel to increase the outside diameter of the annularly shaped element. One such technique is the Poroflex® product from Halliburton, which uses a solid ribbed elastomer sleeve that is longitudinally compressed by an advancing swage. The driving of the swage also increases the mandrel diameter. The ribbing allows part of the sleeve to collapse on itself in a series of accordion folds. The forming of the folds is claimed to bridge the annular gap around the mandrel. The swage is sized so as not to collapse the accordion folds of the collapsed elastomer sleeve. This product is advertised for cased hole applications and appears unsuitable for open hole applications. It also has some uncertainties as to how well it will seal. Longitudinal compression will not always assure that the sleeve will collapse uniformly over the ribbed length. The sealing occurs by end contact of each accordion fold with the casing wall. The number of such ends in contact with the casing wall due to collapse and expansion is uncertain. The possibility, even in cased hole, exists for channeling between the fold ends and the casing wall. The element is not pre-stretched to reduce its run in diameter and therefore can get thinner after swaging to the point where the sealing integrity may be in question. Accordingly, a design is needed that can better address the above described sealing problems in cased hole and that has the ability to seal effectively in open hole.
The present invention employs an annular sleeve as the sealing element and mounts a biasing element with it. The biasing element stores a force, which is liberated downhole to longitudinally compress the element and increase its diameter. In a preferred embodiment the advancing swage liberates a stored force to allow the element diameter to grow to its relaxed dimension. Preferably, the advancing swage liberates this force and increases the mandrel dimension when the element is already at its relaxed diameter forcing the element into the borehole wall or the casing. How this is accomplished, so that those skilled in the art will readily appreciate the scope of the invention, will be explained more fully in the detailed description of the preferred embodiment and the claims, which appear below.
Relevant to the general area of sealing devices, with some illustrating downhole applications are U.S. Pat. Nos. 2,449,514; 4,545,433; 5,062,482; 6,543,780 B1 and Re. 32,831.